Production of cube-on-edge oriented silicon iron



United States Patent 3,115,430 PRODUCTION OF CUBE-ON-EDGE ORIENTED SILICON IRON John M. Jackson and Dale M. Kohler, llliddletown, Ohio, assignors to Armco Steel Corporation, Middletown, Ohio, a corporation of Ohio No Drawing. Filed Sept. 20, 1960, Ser. No. 57,164 5 Claims. (Cl. 1482) The invention relates to silicon-iron sheet stock having good permeability in the rolling direction. This permeability is the result of a preferred crystal orientation of the cube-on-edge type or, in the notation of Millers indices, an orientation of the (110) [001] type.

In the past there have been various ways of making silicon-iron sheet stock in the cube-on-edge orientation, most of these involving hot rolling the steel to an intermediate gauge, annealing it, cold rolling it to final gauge in a plurality of stages with an intermediate anneal, decarburizing it, and then subjecting the material to a final box anneal for the development of its ultimate magnetic properties.

One of the objects of this invention is to provide a silicon-iron sheet material having superior permeability in the rolling direction.

Another object of the invention is to provide a method of making silicon-iron sheet stock characterized by a (110)[00l] orientation in a cheaper and more direct fashion.

It is yet another object of the invention to provide a silicon-iron sheet stock having the desired orientation by a series of cold rolling reductions, with suitable intermediate and final anneals, but without the necessity of hot rolling. In this way, the product can be produced in fair quantity, without the utilization of exceedingly expensive apparatus, including the usual ingot molds, soaking pits, blooming mills, and hot strip mills.

These and other objects of the invention which will be set forth hereinafter or Will be apparent to one skilled in the art upon reading these specifications, are accomplished by that procedure of which an exemplary embodiment will now be described.

It has hitherto been understood that if silicon-iron is cast into thin ingots, its structure will be characterized by columnar grains growing inwardly from the surfaces of the ingot. In castings having the aforesaid structure, the faces of the cubic crystals lie in substantial parallelism with the broad, flat sides of the casting; but the azimuthal orientation has been substantially completely random. By the careful application of reduction and annealing techniques to such castings, sheet stock can be made which is characterized by such random azimuthal or wagon-wheel orientation; and such essentially nonoriented material is useful in some branches of the electrical arts, including the formation of cores for rotating electrical machinery. The best of such materials have had a straight grain permeability at H oersteds of about 1550 and a cross grain permeability of about 1520, as well as good permeability at angles between these directions. It has not hitherto been seen that thin castings of siliconiron would have any utility other than for the formation of such essentially non-oriented stocks.

A great advantage of the present invention is that it permits the inexpensive formation of cube-on-edge stocks from thin castings.

There have been numerous ways suggested in the art for the direct casting of thin ferrous materials. The present invention is not limited to any of them. One method and apparatus which may be employed is that of U8. Letters Patent No. 2,640,235, dated June 2, 1953, in the name of Hazelett. There is a commercial advantage, of course, in continuous casting; but for purice 2 poses of this invention it is quite possible to make thin castings of sheet width and of sheet length or greater, by providing a mold comprising opposed flat parts resistant to the temperatures of molten silicon-iron. Such molds may be formed of refractory materials, but may also be formed, and preferably, of metals unaffected by the molten silicon-iron and having good heat conductivity. One end of such a mold may be immersed in the molten silicon-iron, and the molten metal may be forced between the mold parts either by drawing a vacuum within the mold, or by exerting pressure on the metal to force it to enter the mold interior.

By silicon-iron for purposes of this invention is meant a ferrous material containing enough silicon to prevent a phase change. This ordinarily will require about 2.5% silicon by weight in the metal. Silicon contents above about 3.5% are not generally desired because the metal becomes more difiiculty workable. However, the upper limit of silicon can be determined by commercial workability of the metal in the apparatus at hand.

By way of example, which is not intended to be limiting, the silicon-iron may preferably contain from about 2.90% to 3.30% silicon, from about 0.01 to 0.04% carbon, (preferably 0.02% to 0.03%), 0.06% to 0.12% manganese, and from about 0.015 to 0.040% sulfur (preferably 0.02% to 0.03%), the remainder being substantially all iron with only such impurities as are conventional in silicon-iron materials. The metal may be refined in the open hearth furnace, by one of the oxygenblowing processes, or in other ways. It may, for example, be melted in an electric furnace, although the expense of such a step is generally not warranted.

In the practice of this invention, the nature of the casting is critical. The product will be carried down to final gauge by a series of three cold reduction stages, as hereinafter' taught. Depending upon the final gauge, this will place a limitation on the thickness of the casting. The castings should have, as produced, a thickness ranging from about 0.1 in. to 0.5 in., but preferably around 0.2 in.

Within the above limits, the actual casting thickness may be determined by the worker in the light of the final desired gauge. The lateral and longitudinal dimensions of the casting, as distinguished from its thickness, do not constitute a limitation on the invention and can be varied in accordance with the availability of molds, or direct casting apparatus.

Castings as hereinabove set forth are given a cold reduction with a ratio of about 3 1. They are then subjected to an intermediate anneal which may be of the order of about l300 to 1800 'F. with about 1500 F. being preferred.

A second cold rolling stage is employed to reduce the material again in a ratio of about 3:1. This is followed by a second intermediate anneal of the type hereinabove described.

In a third or final cold rolling stage, the material is reduced in a ratio of about 2:1. This is followed by a decarburization and a final high temperature anneal at a temperature above 1800 and up to or above about 2200 F.

The first two cold rolling reductions set forth above may be varied in extent from about 40% to about and the final cold rolling stage may be varied from about 40% to about 70%. While these variations are possible, the cold rolling reductions otherwise are critical. The atmospheres for the two intermediate anneals should be neutral or reducing. Various gases may be employed, including such gases as cracked ammonia, partially combusted gases, and the like. Pure hydrogen may be employed if desired. However, the atmosphere in the final material to assume a cube-on-corner orientation. final cold rolling treatment and the recrystallization which follows convert this orientation to the cube-onanneal, or at least in the last part of it, should be an atmosphere of hydrogen.

It will be usual to decarburize the material at some heat treatment stage of the process. The decarburization may be carried out in a strand or continuous anneal in accordance with the teachings of the Carpenter et al. US. Patent No. 2,287,467, issued June 23, 1942. A decarburization just prior to the final anneal is. preferred.

The secondary recrystallization contemplated is a recrystallization which proceeds by grain boundary energy. Such secondary recrystallization will occur at temperatures above about 1800" F. especially with materials of high purity after melting, such as vacuum melted stock, which will attain maximum magnetic properties in an anneal at such temperature. Annealing at higher temperatures, i.e. temperatures up to and somewhat above 2200 F. tend to purify the metal, and hence are recommended for materials made by open hearth and other conventional refining procedures.

The mechanism of crystal change in the process of the present invention is believed to be as follows: The type of orientation obtained in the castings has already been described. It has been discovered that when a material having this orientation is subjected to a first cold rolling reduction and an intermediate anneal as described, surprisingly, the grain structure and orientation as well as the distribution of impurities are similar to the best hot rolled materials hitherto produced for making cube-onedge stock. The second cold rolling stage and second intermediate anneal, as hereinabove set forth, cause the The edge type with good azimuthal alignment. The secondary recrystallization causes substantially perfectly oriented cube-on-edge crystals to grow at the expense of other crystals in the material.

Example A casting having a thickness of 0.190 inch was formed by drawing molten metal up into the interior of a thin mold by means of a vacuum, the mold being tormed of plates having a separation of 0.2 inch, as described above. When the mold Was full, it was removed from contact with the molten metal bath and cooling proceeded very rapidly. A first cold rolling reduced the casting to a sheet material of about 0.1 inch, and the second cold rolling reduced it to about 0.025 inch. Intenmediate anneals at about 1500" F. followed each of the first two cold rolling stages. The third cold rolling stage reduced the material to a final gauge of about 0.012 inch. The material was then decarburized in wet hydrogen at 1500 F.,

4 as described, and subjected to a final secondary recrystallization anneal at about 2200 F.

In the above example the two intermediate anneals were open or continuous anneals, as was the decarburization treatment. The final anneal was a box anneal.

If desired, the casting could have been given an anneal prior to the first cold rolling; but this is not ordinarily necessary.

The material treated as above had a permeability at H =10 oersteds of 1800, in the straight grain or rolling direction.

Modifications may be made in the invention without departing from the spirit of it. The invention having been described in an exemplary embodiment, what is claimed as new and desired to be secured by Letters Patent is:

l. A process of making silicon-iron sheet stock having (110) [001] orientation which comprises casting sili con-iron containing sufiicient silicon to prevent phase change into a casting having a thickness ranging from substantially .5 inch to .1 inch and substantially greater breadth and length, cooling the said casting rapidly, and thereafter subjecting the said casting to a first cold rolling reduction of the order of 40% to 80%, an intermediate anneal at from about 1300" to 1800 F., a second cold rolling reduction of about 40% to 80%, a second intermediate anneal at about1300 to 1800 F., a final cold rolling reduction of about 40% to and a final anneal at a temperature above about 1800 F.

2. The process claimed in claim 1 wherein the casting is annealed prior to the first cold rolling reduction.

3. The process claimed in claim 1 wherein the material is decarburized at the final gauge.

4. The process claimed in claim 1 in which the first two mentioned cold rolling reductions have a ratio of about 3:1 and the third mentioned cold rolling reduction has a ratio of about 2: 1.

5. The process claimed in claim 1 wherein the casting is about 0.2 inch thick, wherein it is reduced in the first cold rolling stage to a thickness of about 0.1 inch, Wherein it is reduced in the second stage of cold rolling to about .025 inch, and wherein it is reduced in the third stage of cold rolling to a final thickness of about 0.012 inch.

References Cited in the file of this patent UNITED STATES PATENTS 2,599,340 Littmann et al. June 3, 1952 2,811,759 Pearce Nov. 5, 1957 2,891,883 Howe June 23, 1959 2,940,881 Hollomon June 14, 1960 3,008,857 Mobius Nov. 14, 1961 

1. A PROCESS OF MAKING SILICON-IRON SHEET STOCK HAVING (110)(001) ORIENTATION WHICH COMPRISES CASTING SILICON-IRON CONTAINING SUFFICIENT SILICON TO PREVENT PHASE CHANGE INTO A CASTING HAVING A THICKNESS RANGING FROM SUBSTANTIALLY .5 INCH TO .1 INCH AND SUBSTANTIALLY GREATER BREADTH AND LENGTH, COOLING THE SAID CASTING RAPIDLY, AND THEREAFTER SUBJECTING THE SAID CASTING TO A FIRST COLD ROLLING REDUCTION OF THE ORDER OF 40% TO 80%, AND INTERMEDIATE ANNEAL AT FROM ABOUT 1300* TO 1800*F., A SECOND COLD ROLLING REDUCTION OF ABOUT 40% TO .80%, A SECOND INTERMEDIATE ANNEAL AT ABOUT 1300* TO 1800*F., A FINAL COLD ROLLING REDUCTION OF ABOUT 40% TO 70%, AND A FINAL ANNEAL AT A TEMPERATURE ABOVE ABOUT 1800*F. 